Catalytic cracking of hydrocarbon oils utilizing crystalline zeolites is a known process, practiced for example, in fluid-bed catalytic cracking (FCC) units, moving bed or thermofor catalytic cracking (TCC) reactors, and fixed-bed crackers.
Crystalline zeolites have been found to be particularly effective for the catalytic cracking of a gas oil to produce motor fuels, and have been described and claimed in many patents, including U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,252; 3,140,253; and 3,271,418. It is also known in the prior art to incorporate the crystalline zeolite into a matrix for catalytic cracking, and such disclosure appears in one or more of the above-identified U.S. patents.
It is also known that improved results will be obtained with regard to the catalytic cracking of gas oils if a crystalline zeolite having a pore size of less than 7 Angstrom units is included with a crystalline zeolite with or without a matrix. A disclosure of this type is found in U.S. Pat. No. 3,769,202. Although the incorporation of a crystalline zeolite having a pore size of less than 7 Angstrom units into a catalyst composite comprising a large-pore size crystalline zeolite (pore size greater than 8 Angstrom units) has indeed been very effective with respect to raising the octane number, nevertheless it did so at the expense of the overall yield of gasoline.
Improved results in catalytic cracking with respect to both octane number and overall yield were achieved in U.S. Pat. No. 3,758,403. In the '403 patent, the cracking catalyst comprised a large-pore size crystalline zeolite (pore size greater than 7 Angstrom units) in admixture with a ZSM-5 zeolite, wherein the ratio of ZSM-5 zeolite to large-pore size crystalline zeolite was in the range of 1:10 to 3:1. Effective cracking processes were disclosed as being achieved when the catalyst was used to obtain the inherent advantages realized in moving bed techniques, such as the thermofor catalytic cracking process (TCC), as well as in fluidized cracking processes (FCC).
The use of ZSM-5 zeolite in conjunction with a zeolite cracking catalyst of the X or Y faujasite variety is described in U.S. Pat. Nos. 3 894 931; 3,894,933; and 3,894,934. The former two patents disclose the use of a ZSM-5 zeolite in amounts of about 5-10 wt.%; the latter patent discloses the weight ratio of ZSM-5 zeolite to large-pore size crystalline zeolite within the range of 1:10 to 3:1.
The addition of a separate additive or composite catalyst comprising ZSM-5 has been found to be extremely efficient as an octane and total yield improver, when used in very small amounts, in conjunction with a conventional cracking catalyst. Thus, in U.S. Pat. No. 4,309,279, it was found that only 0.1 to 0.5 wt.% of a ZSM-5 catalyst, added to a conventional cracking catalyst under 1-3 RON+O (Research Octane Number Without Lead).
U.S. Pat. No. 4,309,280 also teaches ZSM-5 and other zeolites in conjunction with a conventional cracking catalyst.
U.S. Pat. No. 4,740,292 to Chen et al. discloses catalytic cracking with a mixture of zeolite Beta and a faujasite zeolite.
U.S. Pat. Nos. 4,309,279; 4,309,280; and 4,521,298 disclose catalytic cracking processes characterized by the addition of very small amounts of additive promoter comprising a class of zeolites having a Constraint Index of about 1 to 12 to cracking catalysts.
U S. Pat. No. 4,416,765 discloses catalytic cracking using a catalyst comprising an amorphous cracking catalyst and a minor amount of a class of crystalline zeolites characterized by a silica to alumina ratio greater than about 12 and a Constraint Index of about 1 to 12.